1. Field of the Invention
The invention relates generally to the manufacturing processes and structures of semiconductor power devices. More particularly, this invention relates to manufacturing processes and structural configurations of improved deep contact trench with reduced critical dimension having shrunken distance between the deep trench contacts.
2. Description of the Prior Art
Conventional methods of manufacturing semiconductor power device are still confronted with technical limitations to make electrical contact in trenches with high aspect ratio and small pitches between these trenches. The technical limitations often become a bottleneck that hinders further reductions of the size and dimension of the electronic device. For these reasons, many techniques have been applied in attempt to overcome these limitations.
Conventional technologies by applying the photolithographic processes are employed to define patterns for opening contact trenches. Typically, photoresist layers are deposited and patterned by selectively exposing the photoresist layer by applying masks to define locations for opening the contact trenches. However, such processes are limited due to the difficulties of properly alignments. Furthermore, the depth of focus and the resolutions of the photolithographic exposures also cause deviations and inaccuracies that demand manufacturing tolerances and hinder the abilities of the manufacturing processes to fabricate device that have contact trenches with submicron pitches.
In U.S. Pat. No. 8,629,019 Xu et al. disclose a method for manufacturing self-aligned contacts for a trench power MOSFET. The method includes, etching trenches in a substrate through a mask of silicon nitride deposited on an oxide layer, forming a gate oxide layer on the walls of the trenches. The gate oxide layer on the sidewalls of the trenches is then applied to self-align the gate bus by filling the gate trenches with a polysilicon layer. Similarly, contact windows to source and body regions are also defined in a silicon nitride for etching the silicon nitride on top of an oxide layer covering over the source and body region. Spacers are grown on sidewalls of these contact windows to self-align the contact metal deposited into these contact windows formed as trenches in the silicon nitride layer having spacers on the sidewalls. The methods disclosed by Xu et al. as disclosed in the patented invention are still limited by the fact that masks are applied first to define the locations on the silicon nitride layer covering over the top surface of the device. Due to the tolerance that is required for allowing small degrees of inaccuracy for the placement of the mask on a flat surface, there are still limit that would hinder the reductions of the pitches between the trench contacts. Even though different contact metals as that disclosed by Xu et al. are formed in the contact trenches in a self-aligned fashion, the contact trenches themselves are not formed by applying a self-aligned process.
Therefore, a need still exists for the ordinary skill in the art to improve the methods of manufacturing of the power devices, particularly the trench contacts to be accurately formed at different locations over the entire top surface area of the power device to resolve these technical limitations. It is the purpose of this invention to provide new and improved methods of manufacturing, structural features and device configurations to precisely place the contact trenches by a self-aligned process such that the above-discussed difficulties and limitations can be overcome.